// Copyright (c) Epic Games Tools
// Licensed under the MIT license (https://opensource.org/license/mit/)

#undef LAYER_COLOR
#define LAYER_COLOR 0xfffa00ff

////////////////////////////////
//~ rjf: Top-Level API

internal void
fs_init(void)
{
  Arena *arena = arena_alloc();
  fs_shared = push_array(arena, FS_Shared, 1);
  fs_shared->arena = arena;
  fs_shared->change_gen = 1;
  fs_shared->slots_count = 1024;
  fs_shared->slots = push_array(arena, FS_Slot, fs_shared->slots_count);
  fs_shared->stripes = stripe_array_alloc(arena);
}

////////////////////////////////
//~ rjf: Change Generation

internal U64
fs_change_gen(void)
{
  return ins_atomic_u64_eval(&fs_shared->change_gen);
}

////////////////////////////////
//~ rjf: Cache Interaction

internal C_Key
fs_content_key_from_artifact_key(String8 key)
{
  C_Key content_key = {0};
  {
    content_key.id.u128[0] = u128_hash_from_str8(key);
  }
  return content_key;
}

internal AC_Artifact
fs_artifact_create(String8 key, B32 *retry_out)
{
  ProfBeginFunction();
  Temp scratch = scratch_begin(0, 0);
  
  //- rjf: unpack key
  String8 path = {0};
  Rng1U64 range = {0};
  {
    U64 key_read_off = 0;
    key_read_off += str8_deserial_read_struct(key, key_read_off, &path.size);
    path.str = push_array(scratch.arena, U8, path.size);
    key_read_off += str8_deserial_read(key, key_read_off, path.str, path.size, 1);
    key_read_off += str8_deserial_read_struct(key, key_read_off, &range);
  }
  
  //- rjf: measure file properties *before* read
  FileProperties pre_props = {0};
  if(lane_idx() == 0)
  {
    pre_props = os_properties_from_file_path(path);
  }
  
  //- rjf: setup output data
  Arena *data_arena = 0;
  U64 data_buffer_size = 0;
  U8 *data_buffer = 0;
  if(lane_idx() == 0)
  {
    U64 range_size = dim_1u64(range);
    U64 read_size = Min(pre_props.size - range.min, range_size);
    U64 data_arena_size = read_size+ARENA_HEADER_SIZE;
    data_arena_size += KB(4)-1;
    data_arena_size -= data_arena_size%KB(4);
    data_arena = arena_alloc(.reserve_size = data_arena_size, .commit_size = data_arena_size);
    data_buffer_size = read_size;
    data_buffer = push_array_no_zero(data_arena, U8, data_buffer_size);
  }
  lane_sync_u64(&data_buffer, 0);
  lane_sync_u64(&data_buffer_size, 0);
  
  //- rjf: open file
  OS_Handle file = {0};
  if(lane_idx() == 0)
  {
    file = os_file_open(OS_AccessFlag_Read|OS_AccessFlag_ShareRead|OS_AccessFlag_ShareWrite, path);
  }
  lane_sync_u64(&file, 0);
  B32 file_handle_is_valid = !os_handle_match(os_handle_zero(), file);
  
  //- rjf: do read
  U64 total_bytes_read = 0;
  U64 *total_bytes_read_ptr = 0;
  if(lane_idx() == 0)
  {
    total_bytes_read_ptr = &total_bytes_read;
  }
  lane_sync_u64(&total_bytes_read_ptr, 0);
  ProfScope("read \"%.*s\" [0x%I64x, 0x%I64x)", str8_varg(path), range.min, range.max)
  {
    Rng1U64 lane_read_range = lane_range(data_buffer_size);
    U64 bytes_read = os_file_read(file, shift_1u64(lane_read_range, range.min), data_buffer + lane_read_range.min);
    ins_atomic_u64_add_eval(total_bytes_read_ptr, bytes_read);
  }
  lane_sync();
  lane_sync_u64(&total_bytes_read, 0);
  
  //- rjf: close file
  if(lane_idx() == 0)
  {
    os_file_close(file);
  }
  
  //- rjf: measure file properties *after* read
  FileProperties post_props = {0};
  if(lane_idx() == 0)
  {
    post_props = os_properties_from_file_path(path);
  }
  
  //- rjf: form content key
  C_Key content_key = fs_content_key_from_artifact_key(key);
  
  //- rjf: abort if modification timestamps or sizes differ - we did not successfully read the file;
  //       otherwise submit data
  B32 read_good = 0;
  if(lane_idx() == 0)
  {
    read_good = (pre_props.modified == post_props.modified &&
                 pre_props.size == post_props.size &&
                 data_buffer_size == total_bytes_read &&
                 (file_handle_is_valid || pre_props.flags & FilePropertyFlag_IsFolder));
    if(!read_good)
    {
      retry_out[0] = 1;
      ProfScope("abort")
      {
        arena_release(data_arena);
        MemoryZeroStruct(&content_key);
      }
    }
    else
    {
      ProfScope("submit")
      {
        c_submit_data(content_key, &data_arena, str8(data_buffer, data_buffer_size));
      }
    }
  }
  lane_sync();
  
  //- rjf: if the read was good, record this path's timestamp in this layer's path info cache
  U64 path_hash = u64_hash_from_str8(path);
  if(lane_idx() == 0 && read_good)
  {
    U64 slot_idx = path_hash%fs_shared->slots_count;
    FS_Slot *slot = &fs_shared->slots[slot_idx];
    Stripe *stripe = stripe_from_slot_idx(&fs_shared->stripes, slot_idx);
    RWMutexScope(stripe->rw_mutex, 1)
    {
      FS_Node *node = 0;
      for(FS_Node *n = slot->first; n != 0; n = n->next)
      {
        if(str8_match(n->path, path, 0))
        {
          node = n;
          break;
        }
      }
      if(node == 0)
      {
        node = stripe->free;
        if(node)
        {
          stripe->free = node->next;
        }
        else
        {
          node = push_array_no_zero(stripe->arena, FS_Node, 1);
        }
        MemoryZeroStruct(node);
        node->path = str8_copy(stripe->arena, path);
        DLLPushBack(slot->first, slot->last, node);
      }
      node->last_modified_timestamp = pre_props.modified;
      node->size = pre_props.size;
    }
  }
  lane_sync();
  
  //- rjf: bundle content key as artifact
  AC_Artifact artifact = {0};
  StaticAssert(sizeof(content_key) == sizeof(artifact), artifact_key_size_check);
  MemoryCopyStruct(&artifact, &content_key);
  
  scratch_end(scratch);
  ProfEnd();
  return artifact;
}

internal void
fs_artifact_destroy(AC_Artifact artifact)
{
  C_Key key = {0};
  MemoryCopyStruct(&key, &artifact);
  key._padding_ = 0;
  c_close_key(key);
}

internal C_Key
fs_key_from_path_range(String8 path, Rng1U64 range, U64 endt_us)
{
  C_Key result = {0};
  Temp scratch = scratch_begin(0, 0);
  Access *access = access_open();
  {
    String8List key_parts = {0};
    str8_list_push(scratch.arena, &key_parts, str8_struct(&path.size));
    str8_list_push(scratch.arena, &key_parts, path);
    str8_list_push(scratch.arena, &key_parts, str8_struct(&range));
    String8 key = str8_list_join(scratch.arena, &key_parts, 0);
    
    //- rjf: find generation number for this key
    U64 gen = 0;
    {
      U64 hash = u64_hash_from_str8(path);
      U64 slot_idx = hash%fs_shared->slots_count;
      FS_Slot *slot = &fs_shared->slots[slot_idx];
      Stripe *stripe = stripe_from_slot_idx(&fs_shared->stripes, slot_idx);
      RWMutexScope(stripe->rw_mutex, 0)
      {
        for(FS_Node *n = slot->first; n != 0; n = n->next)
        {
          if(str8_match(path, n->path, 0))
          {
            gen = n->gen;
            break;
          }
        }
      }
    }
    
    //- rjf: map to artifact
    AC_Artifact artifact = ac_artifact_from_key(access, key, fs_artifact_create, fs_artifact_destroy, endt_us, .gen = gen);
    MemoryCopyStruct(&result, &artifact);
    result._padding_ = 0;
  }
  access_close(access);
  scratch_end(scratch);
  return result;
}

internal U128
fs_hash_from_path_range(String8 path, Rng1U64 range, U64 endt_us)
{
  U128 hash = {0};
  {
    C_Key key = fs_key_from_path_range(path, range, endt_us);
    for EachIndex(rewind_idx, C_KEY_HASH_HISTORY_COUNT)
    {
      hash = c_hash_from_key(key, rewind_idx);
      if(!u128_match(hash, u128_zero()))
      {
        break;
      }
    }
  }
  return hash;
}

////////////////////////////////
//~ rjf: Asynchronous Tick

internal void
fs_async_tick(void)
{
  ProfBeginFunction();
  
  //- rjf: detect changed timestamps for active paths
  {
    Rng1U64 range = lane_range(fs_shared->slots_count);
    for EachInRange(slot_idx, range)
    {
      FS_Slot *slot = &fs_shared->slots[slot_idx];
      Stripe *stripe = stripe_from_slot_idx(&fs_shared->stripes, slot_idx);
      for(B32 write_mode = 0; write_mode <= 1; write_mode += 1)
      {
        B32 found_work = 0;
        RWMutexScope(stripe->rw_mutex, write_mode)
        {
          for(FS_Node *n = slot->first; n != 0; n = n->next)
          {
            FileProperties props = os_properties_from_file_path(n->path);
            if(props.modified != n->last_modified_timestamp)
            {
              found_work = 1;
              if(write_mode)
              {
                n->gen += 1;
              }
            }
          }
        }
        if(!found_work)
        {
          break;
        }
      }
    }
  }
  
#if 0
  Temp scratch = scratch_begin(0, 0);
  
  //- rjf: do detection pass
  {
    U64 slots_per_stripe = fs_shared->slots_count/fs_shared->stripes_count;
    Rng1U64 range = lane_range(fs_shared->stripes_count);
    for EachInRange(stripe_idx, range)
    {
      FS_Stripe *stripe = &fs_shared->stripes[stripe_idx];
      MutexScopeR(stripe->rw_mutex) for(U64 slot_in_stripe_idx = 0; slot_in_stripe_idx < slots_per_stripe; slot_in_stripe_idx += 1)
      {
        U64 slot_idx = stripe_idx*slots_per_stripe + slot_in_stripe_idx;
        FS_Slot *slot = &fs_shared->slots[slot_idx];
        for(FS_Node *n = slot->first; n != 0; n = n->next)
        {
          FileProperties props = os_properties_from_file_path(n->path);
          if(props.modified != n->props.modified)
          {
            for(U64 range_slot_idx = 0; range_slot_idx < n->slots_count; range_slot_idx += 1)
            {
              for(FS_RangeNode *range_n = n->slots[range_slot_idx].first;
                  range_n != 0;
                  range_n = range_n->next)
              {
                C_Key key = c_key_make(n->root, range_n->id);
                if(ins_atomic_u64_eval(&range_n->working_count) == 0)
                {
                  ins_atomic_u64_inc_eval(&range_n->working_count);
                  MutexScope(fs_shared->req_mutex)
                  {
                    FS_RequestNode *req_n = push_array(fs_shared->req_arena, FS_RequestNode, 1);
                    SLLQueuePush(fs_shared->first_req, fs_shared->last_req, req_n);
                    fs_shared->req_count += 1;
                    req_n->v.key = key;
                    req_n->v.path = str8_copy(fs_shared->req_arena, n->path);
                    req_n->v.range = range;
                  }
                }
              }
            }
          }
        }
      }
    }
  }
  
  //- rjf: gather all requests
  local_persist FS_Request *reqs = 0;
  local_persist U64 reqs_count = 0;
  if(lane_idx() == 0) MutexScope(fs_shared->req_mutex)
  {
    reqs_count = fs_shared->req_count;
    reqs = push_array(scratch.arena, FS_Request, reqs_count);
    U64 idx = 0;
    for EachNode(r, FS_RequestNode, fs_shared->first_req)
    {
      MemoryCopyStruct(&reqs[idx], &r->v);
      reqs[idx].path = str8_copy(scratch.arena, reqs[idx].path);
      idx += 1;
    }
    arena_clear(fs_shared->req_arena);
    fs_shared->first_req = fs_shared->last_req = 0;
    fs_shared->req_count = 0;
    fs_shared->lane_req_take_counter = 0;
  }
  lane_sync();
  
  //- rjf: do requests
  for(;;)
  {
    //- rjf: unpack
    U64 req_num = ins_atomic_u64_inc_eval(&fs_shared->lane_req_take_counter);
    if(req_num < 1 || reqs_count < req_num)
    {
      break;
    }
    U64 req_idx = req_num-1;
    FS_Request *r = &reqs[req_idx];
    C_Key key = r->key;
    String8 path = r->path;
    Rng1U64 range = r->range;
    U64 path_hash = fs_little_hash_from_string(path);
    U64 path_slot_idx = path_hash%fs_shared->slots_count;
    U64 path_stripe_idx = path_slot_idx%fs_shared->stripes_count;
    FS_Slot *path_slot = &fs_shared->slots[path_slot_idx];
    FS_Stripe *path_stripe = &fs_shared->stripes[path_stripe_idx];
    
    //- rjf: load
    ProfBegin("load \"%.*s\"", str8_varg(path));
    FileProperties pre_props = os_properties_from_file_path(path);
    U64 range_size = dim_1u64(range);
    U64 read_size = Min(pre_props.size - range.min, range_size);
    OS_Handle file = os_file_open(OS_AccessFlag_Read|OS_AccessFlag_ShareRead|OS_AccessFlag_ShareWrite, path);
    B32 file_handle_is_valid = !os_handle_match(os_handle_zero(), file);
    U64 data_arena_size = read_size+ARENA_HEADER_SIZE;
    data_arena_size += KB(4)-1;
    data_arena_size -= data_arena_size%KB(4);
    ProfBegin("allocate");
    Arena *data_arena = arena_alloc(.reserve_size = data_arena_size, .commit_size = data_arena_size);
    ProfEnd();
    ProfBegin("read");
    String8 data = os_string_from_file_range(data_arena, file, r1u64(range.min, range.min+read_size));
    ProfEnd();
    os_file_close(file);
    FileProperties post_props = os_properties_from_file_path(path);
    
    //- rjf: abort if modification timestamps or sizes differ - we did not successfully read the file
    B32 read_good = (pre_props.modified == post_props.modified &&
                     pre_props.size == post_props.size &&
                     read_size == data.size &&
                     (file_handle_is_valid || pre_props.flags & FilePropertyFlag_IsFolder));
    if(!read_good)
    {
      ProfScope("abort")
      {
        arena_release(data_arena);
        MemoryZeroStruct(&data);
        data_arena = 0;
      }
    }
    
    //- rjf: submit
    else
    {
      ProfScope("submit")
      {
        c_submit_data(key, &data_arena, data);
      }
    }
    
    //- rjf: commit info to cache
    ProfScope("commit to cache") MutexScopeW(path_stripe->rw_mutex)
    {
      FS_Node *node = 0;
      for(FS_Node *n = path_slot->first; n != 0; n = n->next)
      {
        if(str8_match(n->path, path, 0))
        {
          node = n;
          break;
        }
      }
      if(node != 0 && read_good)
      {
        if(node->props.modified != 0)
        {
          ins_atomic_u64_inc_eval(&fs_shared->change_gen);
        }
        node->props = post_props;
      }
    }
    cond_var_broadcast(path_stripe->cv);
  }
  lane_sync();
  
  scratch_end(scratch);
#endif
  ProfEnd();
}